Bicycle crank

ABSTRACT

A bicycle crank with a core comprised of a durofoam substance, a fiber-reinforced plastic coating encasing the core, a bottom bracket axle fitting arrangement foamed into the core accessible through the fiber-reinforced plastic coating, and a bottom bracket axle fitting arrangement foamed into the core accessible through the fiber-reinforced plastic coating.

FIELD OF THE INVENTION

The present invention is directed to a bicycle crank.

BACKGROUND OF THE INVENTION

Bicycle cranks comprised of aluminum alloy castings are known from theprior art, whereby on the one hand, a fitting arrangement is provided atan end of the aluminum alloy casting for the purpose of mounting apedal, and on the other hand, a further fitting arrangement is providedfor the mounting of a pedal spindle. It is also known to fit one or moregear rings on such bicycle cranks.

Disadvantages of the known bicycle cranks have proven to be the heavyweight of the bicycle crank, which in turn can cause problems withrespect to structural strength, and the lack of a simple way to adaptits form to different optical and technical requirements.

SUMMARY OF THE INVENTION

Accordingly, it is a task of the present invention to devise a bicyclecrank and a method for its manufacture which yields a low weight andwhich form can offer versatile design without increased expenditure.

This task is solved through the inventive step of the bicycle crankaccording to the present invention.

Preferred embodiments of the invention comprise the subjects of thedependent claims.

A particular advantage of the bicycle crank according to the presentinvention is that said crank can be manufactured in many differentdesign forms and still maintain low weight and a low apparatusexpenditure.

The density of the carbon-fiber reinforced plastic amounts to only 1550kg/m³, while that of aluminum is approximately 2700 kg/m³. The densityof the durofoam substance is even less. The end result is a dramaticreduction in the weight of the bicycle crank.

The high strength of the carbon-fiber reinforced plastic imparts thebicycle crank according to the present invention with approximately thesame load capacity as conventional castings of aluminum alloy. This hasbeen unequivocally confirmed by the appropriate corresponding load cycletests.

The bicycle crank according to the present invention is simple tomanufacture and provides an especially appealing design function when atransparent plastic is used, which allows the interlocking of the fiberlaminate to be visible from the exterior.

The invention shall be further described in the following on the basisof the preferred embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

It can be seen in the drawings:

FIG. 1 front view of a bicycle crank in accordance with one of the firstpreferred embodiments of the present invention;

FIG. 2 side view of a bicycle crank in accordance with the firstpreferred embodiment of the present invention;

FIG. 3 cross sectional view along the line 3—3 from FIG. 2 of a bicyclecrank in accordance with the first preferred embodiment of the presentinvention;

FIG. 4 further cross sectional view along the line 4—4′ from FIG. 2 of abicycle crank in accordance with the first preferred embodiment of thepresent invention;

FIG. 5 front view of a bicycle crank in accordance with the secondpreferred embodiment of the present invention;

FIG. 6 enlarged partial side view of a bicycle crank in accordance withthe second preferred embodiment of the present invention;

FIG. 7 cross sectional view of a particular preferred embodiment of thebottom bracket axle fitting arrangement of the bicycle crank accordingto the present invention;

FIG. 8 front view of the preferred embodiment of the bottom bracket axlefitting arrangement of the bicycle crank according to the presentinvention;

FIG. 9 cross sectional view of a particular preferred embodiment of thebottom bracket axle fitting arrangement of the bicycle crank accordingto the present invention;

FIG. 10 front view of the preferred embodiment of the bottom bracketaxle fitting arrangement of the bicycle crank according to the presentinvention;

FIG. 11 cross sectional view of a particular preferred embodiment of aninternal thread arrangement as an element of the gear ring fittingarrangement foamed into the durofoam-comprised core of the bicycle crankaccording to the present invention; and

FIG. 12 front view of the preferred embodiment of the internal threadarrangement as an element of the gear ring fitting arrangement foamedinto the durofoam-comprised core of the bicycle crank according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

As the same reference numerals shall consistently refer to the sameelements within the figures, the necessity of a repetitious redundantdiscussion of same is therefore eliminated.

FIG. 1 is a front view of a bicycle crank according to one of the firstpreferred embodiments of the present invention.

FIG. 1 depicts a bicycle crank 1 with a fiber-reinforced plasticcoating. The top side 1 a of the fiber-reinforced plastic coating showsan opening at each end, which in each case provides accessibility for abottom bracket axle fitting arrangement 2 and a bottom bracket axlefitting arrangement 3, both foamed into the core of the bicycle crank 1.

Preferably, the bottom bracket axle fitting arrangement 2 is of lightmetal, in particular an aluminum alloy of essentially cylindricalconfiguration which comprises a square receiving arrangement 4.Preferably, the bottom bracket axle fitting arrangement 3 is alsocomprised of a light metal, in particular an aluminum alloy ofessentially cylindrical configuration which comprises a female threadarrangement 5.

FIG. 2 is a side view of a bicycle crank in accordance with the firstpreferred embodiment of the present invention.

In FIG. 2, 1 b shows the underside of the fiber-reinforced plasticcoating of the bicycle crank 1 according to the present invention. Thedotted lines in FIG. 2 schematically show in each case the position ofthe bottom bracket axle fitting arrangement 2 and the bottom bracketaxle fitting arrangement 3.

The underside 1 b of the fiber-reinforced plastic coating shows two ofthe corresponding openings on the top side 1 a, which in each caseprovides accessibility for a bottom bracket axle fitting arrangement 2and a bottom bracket axle fitting arrangement 3, both foamed into thecore of the bicycle crank 1.

It is to be noted, however, that in principle one opening in thefiber-reinforced plastic coating for the bottom bracket axle fittingarrangement 2 on the underside 1 b, and one opening in thefiber-reinforced plastic coating for the bottom bracket axle fittingarrangement on the top side 1 a would be sufficient.

FIG. 3 is a cross sectional view along line 3—3 of FIG. 2 of a bicyclecrank in accordance with the first preferred embodiment of the presentinvention.

The core 6 of the bicycle crank 1 is comprised of a durofoam material,into which the bottom bracket axle fitting arrangement 2 and the bottombracket axle fitting arrangement 3 are foamed. The durofoam substanceserves to fix the bottom bracket axle fitting arrangement 2 and thebottom bracket axle fitting arrangement 3 and to increase the stiffnessof the entire bicycle crank 1. The durofoam substance preferablyconsists of polyurethane foam.

As is also obvious from FIG. 3, the top side 1 a of the fiber-reinforcedplastic coating consists preferably of a trough-shaped element, whilethe underside 1 b of the fiber-reinforced plastic coating consistspreferably of a flat lid-shaped element joined to it. Both elements aresolidly joined to each other by means of the plastic.

As is expedient, the lid-shaped element shows an overlap edge 7 and iscanted inwardly in the contact joining area 8 with the trough-shapedelement. This additionally increases the stability of the bicycle crank1 and allows for an appealing optical design.

The fiber-reinforced plastic coating may, in general, also be comprisedof several layers of fiber laminate. It is thereby preferable to utilizea plastic which is transparent in order to allow the interlocking of thefiber laminate to be visible to the exterior, thereby providing ainteresting optical appearance.

FIG. 4 is a further cross-sectional view along the line 4—4 in FIG. 2 ofthe bicycle crank according to the first preferred embodiment of thepresent invention.

The cross sectional view shown in FIG. 4. shows the area of the bottombracket axle fitting arrangement 2. It is to be noted, however, that thecorresponding area of the bottom bracket axle fitting arrangement 3 isconstructed analogously.

The bottom bracket axle fitting arrangement 2 is, as mentioned above,preferably of essentially cylindrical configuration. Band-shaped disks 9are positioned at the circumference of the cylinder. These disks 9 serveto increase the connecting solidity of the bottom bracket axle fittingarrangement 2 foamed into the durofoam material, because they enlargethe contact surface in connection with the durofoam material. Inparticular, said durofoam material situated between disks 9 consequentlyprevents a contorting and slipping of the bottom bracket axle fittingarrangement 2.

It should be noted that additional plastic, for example that utilizedfor the fiber-reinforced plastic coating, may be supplementally providedbeyond the durofoam substance itself, in particular in the area of thebottom bracket axle fitting arrangement 2 configuration; said additionalplastic utilized for the purpose of increasing the solidity of theconnection to an even higher degree.

It is further recognized in FIG. 4 that an access opening 10 isconically depressed into the fiber-reinforced plastic coating in thebottom bracket axle fitting arrangement 2 region, as well on the topside 1 a and also on the underside 1 b.

The first preferred embodiment represented in FIGS. 1-4 of the bicyclecable 1 according to the present invention is differentiated for thepedal crank arrangement arranged on the side opposite the chain drive.

A second preferred embodiment of the bicycle cable according to thepresent invention is represented in FIGS. 5 and 6, expedientlydifferentiated for the chain drive side of the of the pedal crankarrangement.

FIG. 5 is a front view of a bicycle cable according to the secondpreferred embodiment of the present invention.

The second preferred embodiment differs from the first preferredembodiment in its design as relates to the configuration in the bottombracket axle fitting arrangement 2 region, as a gear ring arrangement isadditionally provided. However, the connecting surface area and theregion of the bottom bracket axle fitting arrangement area 3 areessentially identical in both preferred embodiments.

Reference numeral 11 in FIG. 5 refers to a bicycle crank with afiber-reinforced plastic coating. The underside 11 b of thefiber-reinforced plastic coating shows an opening at each end exactly asin the first preferred embodiment which in each case providesaccessibility for a bottom bracket axle fitting arrangement 2 and abottom bracket axle fitting arrangement 3, both foamed into the core ofthe bicycle crank 1.

Said second preferred embodiment of the bicycle crank 10 additionallyshows a gear ring fitting arrangement comprised of two parts.

A first part 12 of the gear ring fitting arrangement contains fivealuminum gear ring female threaded splines foamed into the core,accessible through the fiber-reinforced plastic coating, analogouslyconstructed to the bottom bracket axle fitting arrangement 3, accessiblehowever in the example shown only from the underside 11 b of the bicyclecrank 11. The small gear ring with the smallest diameter is preferablyfastened at these threaded gear ring spline arrangements.

A second part 13 contains five annular plastic extensions, arrangedperipherally about the end of the bicycle crank 10 affixed to the pedalspindle. The large and medium gear rings (compare. FIG. 6) may befastened at these annular extensions.

FIG. 6 is an enlarged partial side view of a bicycle crank in accordancewith the second preferred embodiment of the present invention.

In FIG. 6, the region of the bottom bracket axle fitting arrangement 2and the gear ring fitting arrangement 12,13 are shown at enlarged scale.In each case, reference signs 14, 15 and 16 schematically show only apartial representation of small, medium and large gear rings.

In accordance with the first preferred embodiment described above, thecorresponding form of the bicycle crank 1 on the side opposite the chaindrive is represented left of the vertical center line, whereas thedetailed characteristics of the gear ring fitting arrangement 12,13specified above in reference to FIG. 5 are recognized on the right ofthe vertical center line.

In the following, the foamed bottom bracket axle fitting arrangement,the foamed bottom bracket axle fitting arrangement and the foamed partof the gear ring fitting arrangement will be described in furtherdetail.

FIG. 7 is a cross sectional view of a preferred embodiment of the bottombracket axle fitting arrangement for the bicycle crank according to thepresent invention which can be implemented in both the first as also inthe second preferred embodiment.

As shown in FIG. 7, the essentially cylindrical bottom bracket axlefitting arrangement 2 shows the band-shaped disks 9 circumferentially.Said band-shaped disks serve to provide stabilization within the core ofthe bicycle crank.

The band-shaped disks 9 preferably have different diameters. Thecylinder areas between the disks 9 also preferably have differentdiameters. So that it is possible to precisely optimize the stability ofthe configuration for each individual case.

At both ends of the bottom bracket axle fitting arrangement 2 conicaldepressions are preferably provided having an angel of spread of, forexample, 90°; said depressions intended to simplify the mounting of thepedal spindle.

FIG. 8 is a front view of the preferred embodiment of the bottom bracketaxle fitting arrangement for the bicycle crank according to the presentinvention.

From FIG. 8, a further special feature of the bottom bracket axlefitting arrangement 2 becomes clear. The disks 9 namely showcircumferential recesses 17. These recesses 17 provide for an improvedstabilization against rotations of the bottom bracket axle fittingarrangement 2 about the cylinder longitudinal axis 18, as it is exactlyabout this axis that considerable torques come into play.

In the example shown, the recesses 17 are formed in half-circles and arepositioned tangentially about each cylinder area. This type of recess iseasily produced, for example using milled slots, and it confersoutstanding stability.

Preferably, four recesses 17 are provided, set at 90° from one another.It is furthermore possible to offset the recesses 17 of the variousdisks 9 at staggered angles to each other.

The precise type, number and placement of the recesses is dependent uponthe specific stability requirements of each individual case and allowsfor a plurality of possible modifications.

FIG. 9 is a cross sectional view of a preferred embodiment of the bottombracket axle fitting arrangement 3 for the bicycle crank in accordancewith the present invention which can be implemented with the first aswell as with the second preferred embodiment. FIG. 10 is a correspondingfront view.

The bottom bracket axle fitting arrangement 3 represented in FIGS. 9 and10 is constructed analogous to the bottom bracket axle fittingarrangement 2 as shown in FIGS. 7 and 8. Since it receives less force,its diameter is smaller and has fewer disks 9 than the bottom bracketaxle fitting arrangement 2.

FIG. 11 is a cross sectional view of a particular preferred embodiments,of a female thread arrangement as an element of the gear ring fittingarrangement foamed into the durofoam-comprised core of the bicycle crankaccording to the present invention, which can be implemented with thesecond preferred embodiment. FIG. 12 is a corresponding front view.

The aluminum internal threaded arrangement foamed into the core,accessible through the fiber-reinforced plastic coating, for themounting of the small gear ring, is also constructed analogous to thebottom bracket axle fitting arrangement 2 and the bottom bracket axlefitting arrangement 3. However it has an even smaller diameter and evenfewer disks 9 than the bottom bracket axle fitting arrangement, sinceadditional such configurations are provided, for example five as shownin FIG. 5, among which the load burden is apportioned so that thedemands on an individual configuration are reduced.

In the following, the economical method for manufacture of the bicyclecrank according to the present invention will be further described.

First, one or more fiber laminate layers soaked in non-hardened plasticare inserted into a preset ready mold, preferably of non-hardenedplastic, so as to produce a partially open fiber-reinforced plasticcoating in the mold. The plastic coating formed in this manner is, forexample, trough-shaped.

The configurations of the bottom bracket axle fitting arrangement, ofthe bottom bracket axle fitting arrangement and, if necessary, of thegear ring fitting arrangement are inserted into the partially openfiber-reinforced plastic coating.

If increased stiffness is desired, additional non-hardened plastic canbe added to the form, especially in the regions of the configurations ofthe bottom bracket axle fitting arrangement, the bottom bracket axlefitting arrangement and, if necessary, the gear ring fittingarrangement.

Subsequently, a foaming of the fiber-reinforced plastic coating with thedurofoam material takes place.

The fiber-reinforced plastic coating is then subsequently sealed with atleast one fiber laminate layer drenched in non-hardened plastic. Thiscan in particular transpire so that the trough-shaped element cantsinwards upon its side walls and a lid-shaped fiber layer offiber-reinforced plastic is thermoset upon the canted area, which thenforms an overlap edge with the trough-shaped element.

The final completion of the bicycle crank according to the presentinvention is achieved upon the hardening of the fiber-reinforced plasticand the durofoam.

This type of manufacture with the lid-shaped fiber laminate layer offersan additional increase in edge firmness on the one hand and, on theother hand, a handsome visual appearance.

The depressed openings in the fiber-reinforced plastic coating toprovide accessibility to the bottom bracket axle fitting arrangement,the bottom bracket axle fitting arrangement and, if necessary, the gearring fitting, are expediently hobbed in after hardening.

As described above, the present invention imparts a valuablecontribution to the weight reduction and the design flexibility ofbicycle cranks without thereby increasing their cost expenditure.

What is claimed is:
 1. A bicycle crank comprising: a) a core consistingof a durofoam substance; b) a fiber-reinforced plastic coating encasingthe core; c) a first bottom bracket axle fitting arrangement foamed intothe core and accessible through the fiber-reinforced plastic coating;and d) a second bottom bracket axle fitting arrangement foamed into thecore and accessible through the fiber-reinforced plastic coating.
 2. Thebicycle crank according to claim 1, additionally comprises a gear ringfitting arrangement for mounting of at least one gear ring.
 3. Thebicycle crank according to claim 2, wherein the gear ring fittingarrangement comprises at least a first part foamed into an end of thecore and accessible through the fiber-reinforced plastic coating.
 4. Thebicycle crank according to claim 3, wherein one or more of the firstbottom bracket axle fitting arrangement, the second bottom bracket axlefitting arrangement, and the first part of the gear ring fittingarrangement foamed into the core are of essentially cylindricalconfiguration.
 5. The bicycle crank according to claim 4, whereinband-shaped disks are circumferentially provided on the essentiallycylindrical configuration.
 6. The bicycle crank according to claim 5,wherein the disks have circumferential recesses.
 7. The bicycle crankaccording to claim 6, wherein said recesses are half-circle recesses. 8.The bicycle crank according to claim 7, wherein said half-circlerecesses in the essentially cylindrical configuration are aligned intangential contact.
 9. The bicycle crank according to claim 6, whereinthere are four recesses set at 90° from one another in each band-shapeddisk.
 10. The bicycle crank according to claim 5, wherein theband-shaped disks have varying diameters.
 11. The bicycle crankaccording to claim 10, wherein cylinder regions between the disks havevarying diameters.
 12. The bicycle crank according to claim 3, whereinthe gear ring fitting arrangement additionally comprises a second partof annular elements, arranged about an end of said bicycle crank. 13.The bicycle crank according to claim 12, wherein the annular elementsare comprised of plastic and molded into the fiber-reinforced plasticcoating.
 14. The bicycle crank according to claim 3, wherein one or moreof the first bottom bracket axle fitting arrangement, the second bottombracket axle fitting arrangement, and the first part gear ring fittingarrangement are comprised of aluminum.
 15. The bicycle crank accordingto claim 3, further comprising additional plastic embedded around one ormore of the first bottom bracket axle fitting arrangement, the secondbottom bracket axle fitting arrangement, and the first part of the gearring fitting arrangement foamed into the core.
 16. The bicycle crankaccording to claim 3, wherein the first part of the gear ring fittingarrangement comprises a female thread arrangement.
 17. The bicycle crankaccording to claim 1, wherein the fiber-reinforced plastic coating has atrough-shaped part and an adjoining plate-shaped part.
 18. The bicyclecrank according to claim 17, wherein the trough-shaped part and theplate-shaped part form an overlap.
 19. The bicycle crank according toclaim 1, wherein the durofoam substance is comprised of polyurethanefoam.
 20. The bicycle crank according to claim 1, wherein thefiber-reinforced plastic coating consists of carbon fiber-reinforcedphenol resin or epoxy resin.
 21. The bicycle crank according to claim 1,wherein the fiber-reinforced plastic coating comprises one or more fiberlaminate layers.
 22. The bicycle crank according to claim 1, wherein oneof the bottom bracket axle fitting arrangements comprises a femalethread arrangement.
 23. The bicycle crank according to claim 1, whereinone of the bottom bracket axle fitting arrangements comprises a squarereceiving arrangement.
 24. The bicycle crank according to claim 1,wherein said plastic coating is transparent.
 25. A bicycle crankmanufactured according to a procedure comprising the following steps: i)introducing into a mold at least one fiber laminate layer soaked innon-hardened plastic providing a core with a partially openfiber-reinforced plastic coating; ii) inserting at least a first bottombracket axle fitting arrangement and a second bottom bracket axlefitting arrangement in the partially open fiber-reinforced plasticcoating; iii) foaming a durofoam into the partially openfiber-reinforced plastic coating; iv) sealing the partially openfiber-reinforced plastic coating with at least one further fiberlaminate layer soaked in non-hardened plastic; and v) hardening thenon-hardened plastic and the durofoam.
 26. The bicycle crank accordingto claim 25, further comprising the step of inserting a gear ringfitting arrangement in the partially open fiber-reinforced plasticcoating.
 27. The bicycle crank according to claim 26, further comprisingthe step of the canting of side walls of the partially openfiber-reinforced plastic coating and subsequent thermosetting alid-shaped fiber laminate layer to seal the fiber-reinforced plasticcoating.
 28. The bicycle crank according to claim 27, further comprisingthe step of depressing openings in the fiber-reinforced plastic coatingsubsequent to hardening to provide access for one or more of the firstbottom bracket axle fitting arrangement, the second bottom bracket axlefitting arrangement, and the gear ring fitting arrangement.
 29. Thebicycle crank according to claim 28, wherein the mold into which the atleast one fiber laminate layer soaked in non-hardened plastic isintroduced is preset with non-hardened plastic.
 30. The bicycle crankaccording to claim 29, further comprising step of adding a supplementarynon-hardened plastic in the partially open fiber-reinforced plasticcoating in the region of one or more of the first bottom bracket axlefitting arrangement, the second bottom bracket axle fitting arrangement,and the gear ring fitting arrangement.